[PATCH] D40894: [XRay][compiler-rt+llvm] Update XRay trampoline CFI and register stashing semantics

[David Blaikie via llvm-commits]

Yeah, unfortunately I really know nothing about the CFI side of DWARF... -
I'd throw such things in Peter's direction (but maybe that's just me
confusing the different uses of the CFI acronym... ).

On Wed, Dec 6, 2017 at 10:18 PM Dean Michael Berris via Phabricator <
reviews at reviews.llvm.org> wrote:

> dberris added a reviewer: dblaikie.
> dberris added a subscriber: dblaikie.
> dberris added a comment.
>
> Adding @dblaikie to the review for the CFI directives (please feel free to
> nominate someone else who might know better).
>
> The problem I'm having in particular here is the computation in the
> `ALIGNED_CALL_RAX` macro, where we're doing stack re-alignment just before
> the call to the custom event handler function (line 77). Working offline
> with a teammate here in Sydney, we're prototyping some potential ways of
> doing this correctly but using `.cfi_escape ...` and providing raw DWARF
> opcodes. Ideally I wouldn't have to go through such lengths, but without
> the correct CFI directives and/or DWARF information, debugging XRay
> instrumentation handlers and the trampolines becomes really hard (since the
> CFI directives would probably be wrong).
>
> Before I go uploading a work-in-progress implementation here, is there an
> example somewhere of how to potentially resolve this in assembler?
>
> One sticking point is the fact that there seems to be no way to get the
> current CFI offset from the assembler using either a directive or a special
> macro -- at least not one I can find from the assembler manuals.
>
> Pointers would be most appreciated.
>
>
> https://reviews.llvm.org/D40894
>
>
>
>
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